1. Field of the Invention
The present invention relates generally to medical electronic devices and more specifically relates to cardiac pacing leads.
2. Discussion of the Prior Art
A major advance in the development of endocardial pacing leads is taught by Bisping in U.S. Pat. No. 4,106,512. The Bisping invention provides a helical fixation device to be screwed into the endocardial tissue thereby securing the distal end of the lead both acutely and chronically. A major problem with the endocardial screw-in lead of Bisping and his successors has been obtaining a proper seal at the distal end of the lead to prevent ingress of body fluid into the lead body. At column 5, lines 23-27, Bisping describes the use of a medical adhesive to effect the desired seal.
Copending U.S. patent application Ser. No. 69,948, now abandoned, of Dutcher, et al, assigned to the assignee of the present invention describes a guide seal using a sealing membrane of silicon rubber. Common to the sealing techniques taught by Bisping, Dutcher, et al, and others studied is the problem of leakage during chronic implantation.